1. Field of the invention
This invention relates to a vapor condenser for use in a vacuum apparatus, and in particular, to some improvement of the vapor condenser especially developed by the present applicant before and mentioned in Japanese Patent Publication No. 58-12042 equivalent to U.S. Pat. No. 4,407,140 (hereinafter sometimes called the "prior invention").
2. Description of the Prior Art
A vapor condenser (hereinafter sometimes called the "trap") for use in a vacuum apparatus is widely used for the purpose of condensing and trapping the vapor of water and other solvent generated from the material to be treated within a vacuum chamber on a refrigerated surface. Thus, vacuum pressure in the vacuum chamber will be maintained at a desired value. This vapor condenser is constituting the essential part of the vacuum apparatus such as vacuum freeze drying apparatus, vacuum drying apparatus, vacuum concentration, vacuum distillation, vacuum cooling, desolvent or the like.
The trap in a vacuum apparatus, from the viewpoint of theory of heat transfer engineering, may be considered as a sort of heat exchanger between a low temperature medium (refrigerant, the first medium) and a high temperature medium (vacuum vapor, the second medium). And the refrigeration condensing vacuum vapor is provided from low tempeature of refrigerator unites. For the heat exchanger with form of heat transfer, heat flux is transferred through a boundary metal wall from high temperature fluid to low temperature medium. There are three types for the heat exchanger. The first, direct transfer type (heat is exchanging directly between the high and the low temperature medium), the second, indirect type (heat is exchanging indirectly by circulating a middle fluid between the high and the low temperature medium), and the third, triple heat exchanger type (three medium heat exchange).
Three types of the trap (vapor condenser) from FIG. 1 to FIG. 3 will be explained by means of each view illustrating roughly the vapor condenser for use in the vacuum freeze drying apparatus for medical products together with the basic construction of the apparatus as a whole.
FIG. 1 denotes a universally utilized standard type one in which a trap 101 is a refrigerant evaporator with the type of refrigerant direct cooling expansion. FIG. 2 shows a locally utilized type one where a trap 102 is of an "indirect brine type" which comprises a circulating brine having been cooled with a refrigerant by means of an outside heat exchanger 7. And, a trap 103 shown in FIG. 3 is of a "three medium heat exchange type" where both the refrigerant and the brine circulate inside thereof.
In FIGS. 1 to 3, each of the vacuum system is composed of a vacuum drying chamber 1 (which is also used as a freezing chamber), a vacuum trap chamber 2, a main connecting pipe 3a, a main valve 3, a vacuum exhausting system 4 and so on (including the profile of the chamber, machinery and piping). It is wholly indicated with a thin
On the other hand, a freezing refrigerant circulating system including a refrigerator unit 11 (which includes all of a compressor, an oil separator, a condenser, an intermediate cooler used in the case of two-stage compressions, etc., and further includes the case of double freezing), a secondary refrigeration unit 12, a heat exchanger 7 for refrigerant evaporator 7a, a secondary heat exchanger 8 for refrigerant evaporator 8a, the trap 101 of refrigerant direct cooling type, the trap 103 of the prior invention (U.S. Pat. No. 4,407,140), each refrigerant evaporator, a refrigerant pipeline, a refrigerant valve 13, a refrigerant expansion valve 14 (indicated with a triangle mark), etc., is wholly indicated with a broken line.
The brine-system machinery including a shelf 5 (a plate which supplies a latent heat necessary for drying the material to be treated and supplies a cooling heat necessary for pre-freezing the material being treated in the instances of FIGS. 1 to 3), a brine heater 6, a brine system 7b of the heat exchanger 7, a brine system 8b of the secondary heat exchanger 8, the trap 102 of indirect brine type and the trap 103 of the U.S. Pat. No. 4,407,140, a brine pump 9 for use in the shelf and a brine pump 10 for use in the trap and the arrangement are wholly indicated by a thick line.
In FIG. 2 and FIG. 3, furthermore, 15 shows a sluice valve provided in the brine circulating system. In this connection, however, it should be noted that the piping line in each system, the valves and the machinery arrangement sequence in the pipe line are not actually as shown in drawings, in other words drawings are simplified by the way of the explanation within the U.S. Pat. No. 4,407,140.
FIG. 4 and FIG. 5 have shown each view roughly illustrating the vertical section (line A--A of FIG. 5) and the transverse section (line C--C of FIG. 4) of the trap chamber 2 and trap 103 of vacuum freeze dryer illustrated in FIG. 3. A thin broken line shown within a trap plate of FIG. 4 indicates a flow passage of refrigerant R (which corresponds to the refrigerant cooling coils denoted with the numeral 26 in FIG. 6). The rough broken line indicates a boundary of flow passage of brine within the plate (which corresponds to a partition wall denoted with the numeral 27 in FIG. 6), and FIG. 6 is a view illustrating one embodiment of the section of this plate.
One form of a condensing plate X of the trap 103 (vapor condenser) is shown in FIG. 4, and FIG. 7 illustrates another embodiment of a small-sized trap where the inner wall of the vacuum trap chamber is constituted into cylinder. In both situations, a refrigerant evaporation coil 26 is closely contacted with the trap (vapor condensing plate) 103 by welding, press, fitting and the like, and the condensing plate X of the trap 103 performs as heat transfer fin of refrigerant R. Heat exchanges between refrigerant R and brine B through a refrigerant coil wall and the trap 103 as a fin plate, between brine B and vapor V through the condensing plate X of the trap 103 as a brine wall, and between refrigerant R and vapor V through the condensing plate X of the trap 103 as a fin of refrigerant coil 26, respectively. Thus, heat exchange is effected between two mediums selected optionally from among three mediums, namely R, B and V through a boundary metal wall or fin plate. 28 is an outer wall of the vacuum trap chamber 2.
The trap in vacuum apparatus as shown in FIG. 1 to FIG. 3, which is a refrigerant evaporator of refrigeration unit, is usually arranged in the trap chamber. In FIG. 1, the trap with "refrigerant direct cooling type" is utilized. As shown in FIG. 2, brine being cooled by a cooler outside vacuum trap chamber by means of the heat exchanger 7 (hereinafter sometimes called the "cooler 7") of refrigerant evaporator 7a and a circulating circuit of medium fluid of the trap including a brine pump 10 is circulated through the trap 102 with "indirect brine type" in the vacuum trap chamber 2, and a "three medium heat exchange type" where both the refrigerant and the brine circulate inside thereof is utilized as shown in FIG. 3.
For the first form utilizing the trap 101 with "refrigerant direct cooling type", there are some drawbacks, such as, shortage of the operational stability, uneasiness of maintenance, and difficult in controlling the temperature of the vapor condenser, the necessaries of additional secondary refrigeration units and secondary heat exchangers. In the second form utilizing the trap 102 with "indirect brine type", although the said defects of the first form may be improved, some disadvantageous have been occurred in that the presence of the following two refrigeration capacity losses. The first loss is a temperature loss induced through the boundary film heat transfer occurred twice between the refrigerant coil surface and the brine and brine trap surface and brine duo to a indirect heat exchanging between the refrigerant and the condensing surface of the trap. And in external heat exchanger 7, in order to increase the heat exchange between the refrigerant evaporator 7a and the brine and enhance the convection heat transfer coefficient of the brine, and to circulate the brine having been cooled in the external heat exchanger 7 through the trap 102, a large capacity brine pump 10 is necessary for a small temperature difference between inlet and outlet of the trap 102, thus, the second refrigeration capacity loss is occurred. Moreover, because of the brine machinery arrangement including the large-sized heat exchanger 7 and the brine pump 10 and the sluice valve 15 arrangement in the pipeline out of the vacuum trap chamber 2, a large amount of input heat loss will be caused. A larger installation area and excessive energy consumption is called for.
The third form utilizing the trap 103 with "three medium's heat exchange type" is the invention developed before by the present applicant and explained in U.S. Pat. No. 4,407,140. As shown in FIG. 3, it has improved the defects of the trap 101 with refrigerant direct cooling type by means of the arrangement of a trap circulating brine circuit as that of the second form fore-mentioned. Moreover, the heat exchanger between the refrigerant evaporator and the brine is arranged within vacuum trap chamber 2. Thus the drawbacks of the trap with "indirect brine type" in the second form were improved by means of the trap 103 with "three medium heat exchange type" where the vapor is cooled from both sides of the refrigerant and the brine even independently of its companion medium. This form has already been popularized in the vacuum freeze drying apparatus for pharmaceutical products. Especially in Japan it is occupying a principle position instead of the usual two forms of the refrigerant direct cooling type and indirect brine type mentioned above.
Although the third form trap 103 in the prior invention is a heat exchanger between three mediums where also between two mediums selected optionally from among three mediums including the refrigerant, the brine and the vacuum vapor there exists a direct heat exchange through a boundary metal wall or a metal plate closely contacting therewith, a part of the refrigeration capacity necessary for condensing will have a heat exchange with the vacuum vapor on the condensing surface of trap 103 from the refrigerant cooling coils by direct expansion. And another part of cooling heat flux will transfer to the condensing surface of the trap by way of the circulated brine when condensing the vacuum vapor. Therefore, efficient for trap condensing vacuum vapor is depending on heat flux exchanging directly with vacuum vapor from the refrigerant and on heat flux exchanging with vacuum vapor by way of the circulated brine. And, the heat flux transferred by way of the circulated brine is closely related to the boundary film heat transfer coefficient of the brine.
However, the vapor trap plate X of the trap 103 in the prior invention has a too small contact surface between the refrigerant cooling coils 26 of refrigerant evaporator and the metal plate of the trap plate X. Thus, the heat flux exchanging with vacuum vapor V by direct expansion of the refrigerant R decreases, and a large quantity of the refrigeration heat flux exchanges with vacuum vapor V on the condensing surface of vapor trap plate X of trap 103 by way of the circulated brine B.
However, in recent years, silicon oil is being used as the circulating brine B especially in vacuum freeze drying apparatus for treating the material of pharmaceutical products to be dried. This brine B of silicon oil has a high viscosity at low temperature and the boundary film heat transfer coefficient is decreasing. Therefore, as shown in FIG. 8, the vapor trap plate X is constructed by fitting a holding bar 29 in the passage of brine B, installing each two pipes of the refrigerant cooling coils 26 in upper and lower space of bar. A shortage of heat exchange surface of the brine B in passage is improved by using total four pipes of the refrigerant cooling coils 26. However, heat transfer temperature difference loss has been on the increase because of twice boundary film heat transfers by way of the brine. And, accompanied with strengthen of regulation of Freons in refrigerator unites, the low-end evaporation temperature rises for two-stage compression refrigeration system. Because of less heat flux by direct cooling, a fall in boundary film heat transfer coefficient of the circulated brine B and limitation of alternative refrigerants, it is difficult to meet requirement for a lower temperature vapor condenser below -70.degree. C. especially in vacuum freeze drying apparatus.
And, this trap 103 is using the circulating pump 9 as a driving force to circulate the brine in the heat transfer fluid circuit. In this means, necessary capacity of the circulating pump 9 is certainly smaller than in former means for using the trap 102 with indirect brine type, while there is also a refrigeration capacity loss by input heat. However, as for the trap 103 being manufactured according to the prior invention, because the section area of flow passage is too wide, it is necessary to increase the capacity of circulating pump for ensuring an essential boundary film heat transfer coefficient, especially for a brine of silicon oil. Therefore, effective refrigeration capacity of the refrigerant will be decreased and some disadvantageous factors will be caused for the condensing capacity of the trap and low-end trap temperature duo to input heat loss from the circulating pump.